Defrosting arrangement and method for a refrigeration system

ABSTRACT

A defrosting gas is provided in a refrigeration system by compressing a gaseous refrigerant and evaporating controlled amounts of liquid refrigerant carried by the gaseous refrigerant, the latent heat of evaporation being used to defrost the evaporator. The defrosting gas is conducted from the compressor discharge outlet to the evaporator inlet by way of the condenser and the receiver, whereby the accumulation of migratory refrigerant in the receiver is prevented to ensure a sufficient supply of refrigerant in the defrosting circuit throughout the defrosting cycle. Means are provided for operating the system in such a manner.

United States Patent Payne [54] DEFROSTING ARRANGEMENT AND METHOD FOR A REFRIGERATION SYSTEM [72] Inventor: Harold R. Payne, La Habra, Calif.

[73] Assignee: Borg-Warner Corporation, Chicago, Ill.

[22] Filed: Jan. 13, 1971 [21] Appl.No.: 106,190

62/278 51 Int. Cl ..F25b 9/00 58 FieldofSearch ..62/8l,l55,277,278

[56] References Cited UNITED STATES PATENTS 3,038,317 6/1962 Bodcher ..62/277 1 July 18,1972

Halls ..62/8l Harniog ..62/155 Primary ExaminerWilliam J. Wye Attorney-Donald W. Banner and William S. McCurry [57] ABSTRACT A defrosting gas is provided in a refrigeration system by compressing a gaseous refrigerant and evaporating controlled amounts of liquid refrigerant carried by the gaseous refrigerant, the latent heat of evaporation being used to defrost the evaporator. The defrosting gas is conducted from the compressor discharge outlet to the evaporator inlet by way of the condenser and the receiver, whereby the accumulation of migratory refrigerant in the receiver is prevented to ensure a sulficient supply of refrigerant in the defrosting circuit throughout the defrosting cycle. Means are provided for operating the system in such a manner.

5 Claim, 1 Drawing figure PATENTEDJUUBMZ 3.671.025

UVVFNTOR Harold R Payne any/Mid ATTORNEY DEFROSTING ARRANGEMENT AND METHOD FOR A REFRIGERATION SYSTEM BACKGROUND OF THE INVENTION The present invention relates to a method of and means for operating a refrigeration system in a defrosting cycle.

A great many existing refrigeration systems of the vaporcompression type make use of so-called hot gas defrosting in which discharge gas is bypassed from the compressor to the evaporator, where heat is abstracted from the gas to remove accumulated frost and/or ice from the outer surface of the evaporator.

U.S. Pat. No. 2,953,906, issued Sept. 27, 1960 to L. K. Quick, and U.S. Pat. No. 3,163,998, issued Jan. 5, 1965 to D. D. Wile et al. disclose systems in which controlled amounts of liquid refrigerant are carried by the gaseous refrigerant supplied to the compressor suction inlet. The liquid refrigerant is evaporated during compression, and it is primarily the latent heat of evaporation which is abstracted at the evaporator to provide the defrosting effect. Such arrangements provide substantial advantages because they require no external source of defrost heat, because the rate of defrosting is normally uniform and rapid throughout the cycle, and because, since latent heat rather than sensible heat is the primary source of defrosting heat, the defrosting gas need not be delivered to the evaporator at a high temperature, whereby the need for insulating the defrosting gas passage is reduced or eliminated.

In previously know systems, the defrosting gas from the compressor is bypassed to the evaporator inlet, not only around the expansion valve, but also around the condenser and the receiver. Accordingly, in the face of low ambient temperatures refrigerant tends to migrate to the condenser and the receiver where it is reduced to liquid and is collected in the receiver. Under conditions of substantially low ambient temperatures, the amount so collected rapidly becomes excessive and the defrosting circuit is depleted of refrigerant to a point in which liquid refrigerant can no longer be supplied to the compressor. Consequently, only gaseous refrigerant is circulated in the defrosting cycle, and only sensible heat can be abstracted at the evaporator, thereby drastically reducing the rate of defrosting.

SUMMARY OF THE INVENTION It is therefore the object of the present invention to provide a defrosting arrangement and method for a refrigeration system of the type herein described which will provide defrosting at a substantially uniform and rapid rate throughout the defrosting cycle despite the presence of low ambient temperatures.

In accordance with the invention the defrosting gas is passed through the condenser and the receiver before it is conducted to the evaporator, the condenser being inoperative during the defrosting cycle, to maintain the condenser and receiver free of migratory refrigerant.

Also in accordance with the invention, a defrost passage is formed between the compressor discharge outlet and the evaporator inlet by the condenser, the receiver, and a defrost conduit connecting the receiver outlet and the evaporator inlet.

THE DRAWING The FIGURE is a schematic representation of a refrigeration system constructed and adapted to be operated in accordance with the present invention.

THE PREFERRED EMBODIMENT Referring to the drawing, there is shown a refrigeration system in which an expansion valve 1, an evaporator 2, an accumulator 3, a compressor 4, a condenser and a receiver 6 are connected in series in a closed refrigeration circuit for normally conducting any suitable refrigerant in a refrigerating cycle. The position of the expansion valve 1 is dictated by an expansion valve control means la, which is in turn controlled by signals generated by a temperature-sensitive element or bulb 1b and transmitted by way of a control line 1c. The accumulator 3 is enclosed by an accumulator shell 3a, and the receiver 6 is similarly enclosed by a receiver shell 6a, both shells being shown in cross section in the drawing. A dashed line 7 represents a wall or partition which forms a part of the enclosure defining the space to be refrigerated. Such an enclosure normally being constructed to provide thermal insulation, the elements shown to the right of the dashed line 7 are subject to ambient temperatures while the elements shown to the left of the dashed line are subject to the temperatures prevailing within the refrigerated space.

The refrigeration circuit is largely conventional and may be found in many existing systems. More particularly, during operation in the refrigeration cycle, gaseous refrigerant at relatively high temperature and pressure is discharged from the compressor 4 at the compressor discharge outlet 10 and conducted to the condenser inlet 12 by way of a high pressure conduit 14. Cooling air is driven over the outer surface of the condenser 5 by a blower or fan 16, which in turn is driven by a motor 18 powered by any suitable source (not shown) and energized and de-energized by signals transmitted by way of a control line 18a.

The gaseous refrigerant is reduced to liquid in the condenser 5, and the liquid refrigerant is conducted from the condenser outlet 20 to the receiver 6 by way of a condensate conduit 22 and the receiver inlet 24, the receiver 6 providing a reservoir for the storage of liquid refrigerant during operation in the refrigerating cycle. The system is charged with sufficient refrigerant to maintain at least a predetermined minimum level of liquid refrigerant in the receiver 6 at all times during operation in the refrigerating cycle.

Liquid refrigerant is taken from the receiver 6 by way of the receiver outlet 26, which is located substantially below the predetermined minimum level of liquid refrigerant in the receiver, and led through a liquid conduit 28 to the expansion valve 1 where it is expanded to enter the evaporator inlet 30 at reduced pressure.

The liquid refrigerant is evaporated in the evaporator 2 to abstract heat from the refrigerated space, and the resulting vapor or gaseous refrigerant is conducted from the evaporator outlet 32 by way of a low pressure conduit 34 to the accumulator inlet 36 where it enters the interior of the accumulator shell 3a. From here it is drawn through a gas passage, shown in the drawing as an orifice 38, to form a stream of gaseous refrigerant at a relatively low pressure which is withdrawn from the accumulator 3 by way of the accumulator outlet 40 and conducted in a suction conduit 42 to the compressor suction inlet 44. Its temperature and pressure are then elevated in the compressor 4 to repeat the refrigerating cycle.

It will be noted that a portion of the liquid conduit 28 is located within the accumulator shell 3a and is shown in the form of a coil 46 surrounding the accumulator inlet 36. The coil 46 and the accumulator inlet 36 co-operate to form a heat-exchanger which enhances the efficiency of the system during operation in the refrigerating cycle. For ease in reading the drawing, the coil 46 and the accumulator inlet 36 are shown as being spaced from each other; in practice they are positioned in a manner to establish an effective heat-exchange relationship. An example of such a heat-exchanger is described and illustrated with particularity in the aforementioned U.S. Pat. No. 3,163,998.

Like most refrigeration systems of similar type, the present system is provided with a defrosting capability to permit the removal of frost and/or ice accumulated on the outer surface of the evaporator 2. As in such similar systems, the evaporator 2, the accumulator 3 and the compressor 4 are connected in a closed defrost circuit for alternatively and intermittently conducting the refrigerant in a defrosting cycle, a defrost passage being provided between the compressor discharge outlet 10 and the evaporator inlet 30 to bypass the relatively high pressure gaseous refrigerant from the compressor 4 around the expansion valve 1 to the evaporator 2. During operation in the defrosting cycle, the evaporator 2 acts in the manner of a condenser; that is, heat is abstracted from the gaseous refrigerant to remove the frost and/or ice, a portion of the refrigerant consequently being reduced to liquid.

it is well at this point to describe briefly the function of the accumulator 3 during the defrosting cycle. Under normal conditions, the accumulator 3 will be free of liquid refrigerant during the refrigerating cycle. However, during the defrosting cycle liquid refrigerant as well as gaseous refrigerant is delivered to the accumulator 3 from the evaporator 2 by way of the evaporator outlet 32, the low pressure conduit 34 and the accumulator inlet 36. The liquid refrigerant is collected in the lower portion of the accumulator shell 3a while the gaseous refrigerant is drawn through the orifice 38 to form the aforementioned stream of gaseous refrigerant. The liquid refrigerant in the lower portion of the shell 30 is metered or bled through a liquid passage, shown in the drawing as an orifice 48, and introduced into the stream of gaseous refrigerant. Both the gas orifice 38 and the liquid orifice 48 are shown for convenience as being defined by the interior of the shell 30 and a baffle 50. The stream of gaseous refrigerant being withdrawn from the accumulator outlet 40 thus carries a fine suspension of liquid refrigerant to the compressor suction inlet 44 by way of the suction conduit 42. The compression of the stream of gaseous refrigerant in the compressor 4 acts to evaporate the liquid refrigerant carried thereby, and it is primarily the latent heat of evaporation which is abstracted at the evaporator 2 to carry out the defrosting. Evaporation of the liquid refrigerant also acts to cool the compressor 4.

The amounts of liquid refrigerant carried by the stream of gaseous refrigerant must of course be small enough that the compressor 4 will not be damaged. Therefore, the liquid orifice 48 must by carefully sized or calibrated to provide a closely controlled rate of metering or bleeding of liquid refrigerant into the stream of gaseous refrigerant. Accumulators which are suitably constructed for this purpose are shown and described with particularity in the aforementioned U.S. Pat. Nos. 2,953,906 and 3,163,998.

In previously known systems the gaseous refrigerant discharged from the compressor is conducted directly from the compressor discharge outlet, or from a point between the compressor and condenser, to the evaporator inlet, thereby bypassing not only the expansion valve but also the condenser and receiver. However, during operation in the defrosting cycle in the presence of a low ambient temperature, refrigerant migrates to the inoperative condenser and receiver where it is reduced to liquid and collected in the receiver. The amount of refrigerant so collected rapidly becomes excessive during operation under conditions of substantially low ambient temperatures. The defrosting circuit is depleted of refrigerant until the accumulator is no longer able to supply liquid refrigerant to the stream of gaseous refrigerant flowing to the compressor. This results in a condition in which only gaseous refrigerant is circulated in the defrost circuit, whereby only sensible heat can be abstracted in the evaporator and the rate of defrosting is drastically slowed, frequently to the point in which the defrosting effect is imperceptible.

In accordance with the present invention the condenser 5 and the receiver 6 are included in the defrost passage between the compressor discharge outlet 10 and the evaporator inlet 30. More particularly, a defrost conduit 52 is connected at one end thereof to communicate with the receiver outlet 26 and at the other end thereof with the evaporator inlet 30. A defrost valve 54 associated with the defrost conduit 52 has a normally closed position closing the defrost conduit 52 to the passage of refrigerant during operation in the refrigerating cycle, but is movable to an open position to permit the flow of refrigerant through the defrost conduit 52 during operation in the defrosting cycle. The defrost valve 54 is provided with a defrost valve control means 540, which may conveniently comprise a simple solenoid, actuated in response to signals received by way of a defrost valve control line 54b.

A conventional defrost control 56 is provided to generate control signals to the defrost valve control means 54a and the fan motor 18 to initiate and terminate the defrosting cycle. The defrost control 56 typically includes a timing mechanism 58 for initiating the defrosting cycle at predetermined intervals which may be adjusted in accordance with individual requirements and varying conditions. The defrost control 56 also typically includes a thermostat device controlled by signals generated by the temperature-sensitive element lb and transmitted by way of a control line 60a. The thermostat device 60 is adjusted to be sensitive to a predetermined increase in the temperature at the evaporator outlet 32 to actuate the defrost control 56 to terminate the defrosting cycle and initiate the refrigerating cycle. The timing mechanism 58 is preferably adjustable to actuate the defrost control 56 to terminate the defrosting cycle after a further predetermined interval in the event the thermostat device should fail to operate. Although the thermostat device 60 is shown for convenience as being responsive to the temperature-sensitive element 112, it may alternatively be provided with a separate temperature-sensitive element of its own, positioned at the evaporator outlet 32.

OPERATION To initiate the defrosting cycle, the timing mechanism 58 actuates the defrost control 56 to generate a signal to the defrost valve control means 54a, which responds by moving the defrost valve 54 to its open position. Simultaneously the defrost control generates a signal to the fan motor 18 to deenergize the fan motor, thereby rendering the condenser 5 inoperative. The opening of the defrost valve 54 provides a passage between the receiver 6 and the evaporator 2 consisting of the receiver outlet 26 and the defrost conduit 52. At this point the receiver 6 contains at least the aforementioned minimum level of liquid refrigerant maintained during operation in the refrigerating cycle. This liquid refrigerant is now emptied from the receiver 6 by way of the receiver outlet 26 and conducted through the defrost conduit 52 to the evaporator inlet 30. it then passes through the evaporator 30 and is conducted from the evaporator outlet 32 by the low pressure conduit 34 to the accumulator inlet 36 from which it is collected in a body in the lower portion of the accumulator shell 3a. When the receiver 6 is free of liquid refrigerant, or more precisely, when the level of refrigerant in the receiver has fallen below the lower or inner end of the receiver outlet 26, the gaseous refrigerant compressed in the compressor 4 is conducted from the compressor discharge outlet 10 through the high pressure conduit 14 to the condenser inlet 12, passed through the condenser 5 where little if any heat is abstracted since the fan 16 is inoperative, conducted from the condenser outlet 20 by way of the condensate conduit 22 to the receiver inlet 24, passed through the receiver 6, withdrawn from the receiver by way of the receiver outlet 26, conducted through the defrost conduit 52 to the evaporator inlet 30, passed through the evaporator 2, and conducted from the evaporator outlet 32 by way of the low pressure conduit 34 to the accumulator inlet 36. From the accumulator inlet 36, the gaseous refrigerant is drawn through the gas orifice 38 to be directed into the aforementioned stream. Liquid refrigerant from the body collected in the lower portion of the accumulator shell 30 is bled into the stream by way of the calibrated liquid orifice 48, and the liquid-carrying stream is conducted from the accumulator outlet 40 to the compressor suction inlet 44 by way of the suction conduit 42. The gaseous refrigerant is compressed in the compressor 4, and the liquid refrigerant present is evaporated to absorb the latent heat of evaporation. The

resulting defrosting gas is discharged at the compressor discharge outlet 10 to be conducted in the circuit just described through the condenser 5, the receiver 6 and the defrost conduit 52 to the evaporator 2 where the latent heat of evaporation is abstracted to provide the defrosting effect. A portion of the gaseous refrigerant is thereby reduced to liquid in the evaporator 2, and the liquid and gaseous refrigerant are conducted to the accumulator 3 to repeat the cycle.

It should be noted that, owing to pressure conditions, when the defrost valve 54 is first moved to its open position, little or no liquid refrigerant from the receiver 6 will enter the liquid conduit 28. When the liquid refrigerant from the receiver 6 reaches the evaporator outlet 32 at the beginning of the defrosting cycle, the temperature-sensitive element 1b, which is conventionally positioned at the evaporator outlet 32, will generate a signal by way of the expansion valve control line 1c to the expansion valve control means la to close the expansion valve 1, whereby all of the defrosting gas will flow through the defrost conduit 52. However, should the expansion valve I fail to close for any reason, pressure conditions preclude the possibility of any substantial amount of defrosting gas being passed through the liquid line 28.

It will be evident that the defrost passage formed between the compressor discharge outlet and the evaporator inlet 30 by the condenser 5, the receiver 6 and the defrost conduit 52 is so arranged that the accumulation of liquid refrigerant in the receiver 6 is wholly prevented during operation in the defrosting cycle. Thus there will be a sufficient amount of liquid refrigerant present in the accumulator 3 throughout the defrosting cycle to permit the defrosting to proceed at a substantially uniform and rapid rate.

When the thermostat device 60 of the defrost control 56 senses the predetermined temperature at the evaporator outlet 32 which indicates that defrosting has been completed, it actuates the defrost control 56 to generate an appropriate signal to the defrost valve control means 54a, which responds by moving the defrost valve 54 to its closed position. At the same time, the temperature-sensitive element 1b generates a signal to the expansion valve control means la to open the expansion valve 1. Simultaneously with these operations, or after a brief delay, a signal is also generated by the defrost control 56 to the fan motor 18 to energize the fan motor and resume operation of the condenser 5. The system will now be in condition to resume operation in the refrigerating cycle. Liquid refrigerant will continue to be bled from the liquid orifice 48 into the stream of gaseous refrigerant formed by the gas orifice 38 until the accumulator 3 is free of liquid refrigerant. The condenser 5 now being operative, the gaseous refrigerant discharged by the compressor 4 will be reduced to liquid in the condenser S and collected in the receiver 6. When the level of liquid refrigerant in the receiver 6 rises above the open end of the receiver outlet 26, the system will begin to operate in the normal refrigerating cycle.

While the invention has been described in connection with a specific embodiment thereof, it is to be understood that this is by way of illustration and not by way of limitation; and the scope of the appended claims should be construed as broadly as the prior art will permit.

lclaim:

l. A method of operating a refrigeration system in a defrosting cycle, comprising the steps of directing gaseous refrigerant into a stream thereof, metering liquid refrigerant from a body thereof into said stream at a controlled rate, compressing said stream to provide a defrosting gas, conducting the defrosting gas through a condenser to a receiver, withdrawing the defrosting gas from the receiver and passing it through an evaporator to defrost the evaporator, withdrawing liquid and gaseous refrigerant from the evaporator, returning the liquid refrigerant withdrawn from the evaporator to said body of liquid refrigerant, and re-directing the gaseous refrigerant withdrawn from the evaporator into said stream to repeat said defrosting cycle, said steps being carried out with the condenser inoperative.

2. The method according to claim 1 including the preliminary steps of withdrawing liquid refrigerant from the receiver and passing it through the evaporator, withdrawing the liquid refrigerant from the evaporator, and collecting the liquid refrigerant withdrawn from the evaporator to establish said body of liquid refrigerant.

3. In a refrigeration system mcludmg an expansion valve, an

evaporator, a compressor, a condenser communicating with the compressor discharge outlet, a receiver communicating with the condenser outlet, an accumulator arranged to receive refrigerant from the evaporator and adapted to direct gaseous refrigerant into a stream thereof, the accumulator having means for collecting a body of liquid refrigerant and means for metering liquid refrigerant from said body at a predetermined rate into said stream of gaseous refrigerant, a suction conduit for conducting said stream to the compressor suction inlet. means forming a defrost passage between the compressor discharge outlet and the evaporator inlet for bypassing gaseous refrigerant from the compressor around the expansion valve to the evaporator, and a defrost valve associated with the defrost passage for controlling the flow of refrigerant therein; the improvement comprising the feature that said means forming said defrost passage comprise the condenser, the receiver, and a defrost conduit interconnecting the receiver outlet and the evaporator inlet.

4. In a refrigeration system including an expansion valve, an evaporator, an accumulator, a compressor, a condenser and a receiver connected in series in a closed refrigeration circuit for normally conducting refrigerant in a refrigerating cycle; the evaporator, accumulator and compressor also being connected in a closed defrost circuit for alternatively conducting refrigerant in a defrosting cycle; the accumulator being adapted to direct relatively low pressure gaseous refrigerant into a stream thereof, the accumulator having means for collecting a body of liquid refrigerant and means for metering liquid refrigerant from said body at a controlled rate into said stream of gaseous refrigerant; a suction conduit for conducting said stream to the compressor suction inlet; a defrost conduit connected in the defrost circuit for bypassing relatively high pressure gaseous refrigerant from the compressor around the expansion valve to the evaporator; and a defrost valve associated with the defrost conduit and movable between a refrigerating position closing the defrost conduit to the passage of refrigerant and a defrosting position opening the defrost conduit to the passage of refrigerant; the improvement comprising the feature that the defrost conduit interconnects the receiver outlet and the evaporator inlet, whereby when the defrost valve is in its defrosting position, a defrost passage for said high pressure gaseous refrigerant is formed between the compressor discharge outlet and the evaporator inlet by the condenser, the receiver and the defrost conduit.

5. In a refrigeration system according to claim 4, wherein said refrigerant is present in the system in an amount sufficient to maintain a predetermined minimum level of liquid refrigerant in the receiver during operation in the refrigerating cycle, the further improvement comprising the feature that the receiver outlet is located substantially below said predetermined minimum level. 

1. A method of operating a refrigeration system in a defrosting cycle, comprising the steps of directing gaseous refrigerant into a stream thereof, metering liquid refrigerant from a body thereof into said stream at a controlled rate, compressing said stream to provide a defrosting gas, conducting the defrosting gas through a condenser to a receiver, withdrawing the defrosting gas from the receiver and passing it through an evaporator to defrost the evaporator, withdrawing liquid and gaseous refrigerant from the evaporator, returning the liquid refrigerant withdrawn from the evaporator to said body of liquid refrigerant, and re-directing the gaseous refrigerant withdrawn from the evaporator into said stream to repeat said defrosting cycle, said steps being carried out with the condenser inoperative.
 2. The method according to claim 1 including the preliminary steps of withdrawing liquid refrigerant from the receiver and passing it through the evaporator, withdrawing the liquid refrigerant from the evaporator, and collecting the liquid refrigerant withdrawn from the evaporator to establish said body of liquid refrigerant.
 3. In a refrigeration system including an expansion valve, an evaporator, a compressor, a condenser communicating with the compressor discharge outlet, a receiver communicating with the condenser outlet, an accumulator arranged to receive refrigerant from the evaporator and adapted to direct gaseous refrigerant into a stream thereof, the accumulator having means for collecting a body of liquid refrigerant and means for metering liquid refrigerant from said body at a predetermined rate into said stream of gaseous refrigerant, a suction conduit for conducting said stream to the compressor suction inlet, means forming a defrost passage between the compressor discharge outlet and the evaporator inlet for bypassing gaseous refrigerant from the compressor around the expansion valve to the evaporator, and a defrost valve associated with the defrost passage for controlling the flow of refrigerant therein; the improvement comprising the feature that said means forming said defrost passage comprise the condenser, the receiver, and a defrost conduit interconnecting the receiver outlet and the evaporator inlet.
 4. In a refrigeration system including an expansion valve, an evaporator, an accumulator, a compressor, a condenser and a receiver connected in series in a closed refrigeration circuit for normally conducting refrigerant in a refrigerating cycle; the evaporator, accumulator and compressor also being connected in a closed defrost circuit for alternatively conducting refrigerant in a defrosting cycle; the accumulator being adapted to direct relatively low pressure gaseous refrigerant into a stream thereof, the accumulator having means for collecting a body of liquid refrigerant and means for metering liquid refrigerant from said body at a controlled rate into said stream of gaseous refrigerant; a suction conduit for conducting said stream to the compressor suction inlet; a defrost conduit connected in the defrost circuit for bypassing relatively high pressure gaseous refrigerant from the compressor around the expansion valve to the evaporator; and a defrost valve associated with the defrost conduit and movable between a refrigerating position closing the defrost conduit to the passage of refrigerant and a defrosting position opening the defrost conduit to the passage of refrigerant; the improvement comprising the feature that the defrost conduit interconnects the receiver outlet and the evaporator inlet, whereby when the defrost valve is in its defrosting position, a defrost passage for said high pressure gaseous refrigerant is formed between the compressor discharge outlet and the evaporator inlet by the condenser, the receiver and the defrost conduit.
 5. In a refrigeration system according to claim 4, wherein said refrigerant is present in the system in an amount sufficient to maintain a predetermined minimum level of liquid refrigerant in the receiver during operation in the refrigerating cycle, the further improvement comprising the feature that the receiver outlet is located substantially below said predetermined minimum level. 